The Effect of Hypertonicity on the Time Course of the Active State in Single Skeletal Muscle Fibres of the Frog

The time course of the active state was investigated in single skeletal frog muscle fibres in normal Ringer's solution and in Ringer's solution made hypertonic (1.44–1.67 R) by addition of sucrose. During a single, isometric twitch the plateau phase of the active state was abbreviated in hypertonic solution. During repetitive stimulation there was a progressive increase in the duration of the active state and a slowing of the rate of decay of the activity in the hypertonic medium. The resting membrane potential was insignificantly affected by the hypertonic solutions used. There was a slight decrease in overshoot and also a diminution in the rate of rise and rate of decay of the action potential. As a possible explanation of the results, it is suggested that in a hypertonic medium there is a diminished release of calcium in response to a stimulus. This leads to a shortening of the plateau phase of the active state during a single twitch. Because of a reduced rate of re‐uptake of calcium by the sarcoplasmic reticulum, the duration of the active state is prolonged and the decay of activity slowed during repetitive stimulation.